The video: NASA's Cassini orbiter has captured an unprecedented close-up look at the Saturn moon Helene, also known as the "ice queen." The spacecraft passed 4,330 miles away from the 20-mile-wide moon. That wasn't its closest fly-by — in March 2010 it came within 1,131 miles of Helene's surface. But the images Cassini snapped this time were the sharpest and most comprehensive yet, capturing everything from Helene's sunlit side, covered with mysterious gullies, to its dark, crater-pocked side. (See an animation of the photos below.) The new record could help astronomers finish mapping Helene, and shed light on the grooved, pockmarked moon's past.
The reaction: "What a wacky, wacky world Cassini has revealed Helene to be!!" says Emily Lakdawalla at The Planetary Society. If those gullies were seen on Earth, or even Mars, we'd assume they were related to water, but "there is no possibility of liquid water on Helene." Maybe they're formed when dusty stuff cascades toward low points on Helene's surface. This misshapen moon — too small to have the gravity to sculpt it into a sphere — is full of mysteries, says Phil Plait at Discover. For example, why is its bright side so smooth, when most of Saturn's 60 moons are covered with craters? "I've said it before... Saturn's moons are damn weird." Have a look at an animation created by The Planetary Society: